Vacuum tube detector



Nov. 20, 1934. K, c, BLACK VACUUM TUBE DETECTOR Filed April 21, 1930C'arrierM gu Q Flmp lvfwr bra creased Carr/er l o/faqe I i J Qmmntov,Z4: /M W lav Dressed C nrr 'er l/faq 1 I Patented Nov. 20, 1934 UNITEDPATENT rric mesne assignments, to Radio Corporation of Amenca-,New York,N. Y., a corporation of Delaware Application April 21, 1930, Serial No.446,097

11 Claims,

This invention. relates" to vacuum. tube detectors and more particularlyto methodsof and' circuits for obtaining a desired and predeter-' minedvrelationship between: impressed signal voltage and. rectified output.

In accordance with the present invention, Lin-- ear rectification may beeffected over a. wide range or signal voltages by combining grid cirwitand plate rectification in a single rectifier stage; The generalarrangement or the rectifier stage may be stated as comprising two rec'-tifier tubes having their input circuits in parallel and their outputcircuits in. series.

Objects of the invention are to provide improved methods of and circuitsfor? the rectification of alternating voltages, particularly modulatedcarrier wave signals; Further objects are" to" provide methods of andcircuits for the demodulation of signals, which methods and cirv cuitsare characterized: by high: sensitivity andi substantial freedom fromdistortion: over a'- wide range of signal voltages. More: particularly,-objects are to provide methods of demodulation bywhich the relationshipof rectified output to" impressed signal voltage may be adjusted bycombining, in predetermined ratio; the effects of grid and ofplaterectification. 1

These. and: other objectsor the invention-wilt be apparent from thefollowing; specification,-

when taken with the accompanying drawing. in which: I

Fig. 1 is a circuit diagram of? a vacuum tube rectifier stage embodyingthe invention, and

Figs 2 and: 3' are curve sheetsshowing the variation of rectifiedvoutput voltage witlr alternatin'g signal voltage.

As shown inFig. 1, the signal voltage is intpressed, inv parallel; uponthe rectifier tubes: 1 and 2'. The input impedance may takethe form of atransformer secondary 3 which has one terminal connected to the cathodesand which preferably has some provision for receiving adjustable taps 4,5 which lead to the grids ofthe respective tubes 1 and 2; The customarygrid condenser 6 and leak resistance 7 are included in the input circuitof tube 1 and tube 2 is fed: through the blocking condenser 8,1 the biasfor plate rectification being-- applied through a resistor 9 in theusual manner. The respective plate circuits are by-passed for radiofrequency currents by condensers 10, and" the plate voltages aresupplied from a common source 11,- the voltages on the respective platesll being preferably adjustable, by taps 12, 13-, re-

spectively, in order that the tubesmay be individually controlled.

The audio frequency impedances across which the rectified voltages aredeveloped are shown in Fig; I as resistances 14, 15, respectively, butit will be apparent that these impedances may take" the form of chokes,transformers, or other output devices. Ih'e output circuit 16 of thestage may be connected across the plate terminals of th'eresistances14,15, and is shown as an. audio frequency transformer although otherfbrms of audid' frequency impedance may be employed. V

Since the stage" output circuit 16 is connectedacross the seriallyarranged imped'ances 14,. 15 of the individual plate circuits, it willbe apparent that the stage output voltage E is equal to the sum of thevoltage Ekwhich is developed across impedance" 14: by grid circuitrectification, and. the voltage E which is developed across impedance 15by plate circuit rectification.

In Fig; 2, the curve A is the characteristic curve showing therelationship between direct current;- output voltage and unmodulatedradio frequency input'volt'ages 'for the grid circuit rectifier tube 1',and the curve B is a similar curve for the plate rectifier tube 2, Thetotal output voltage E may be determined graphically by combining curvesA and B, and the variation" of the direct current potential drop E withunmodulated input voltages is shown by the curve C. The relativemagnitudes of the input voltages impressed upon the separate tubes maybe-a'dju'sted by the taps 4, 5 of the input circuits, or, when the inputvoltages are identical, the relative magnitudes of the rectifiedvoltages arising from grid and from plate rectification maybe controlledby adjustment of the taps 12,

1 3 which determine the plate voltages of the respective tubes. Eitheror both of these controlmethods may be employed, and, if desired, afurther control may be effected by connecting the" terminals of thestage output circuit 16 to the plate impedances 14, 15' throughadjustable t ps.- 10

In the case of radio receiver operation, it Will usually be preferableto combine the individual rectified voltages E E in such ratio that thecurve for voltage B will take the form shown in Fig. 2 i.- e., linearrectification will obtain over an extended range of appliedalternatingcurrent voltages. The invention is-not limited how-, ever to thisparticular adjustment of the operating conditions of the respectivetubes, since-some other form of characteristic may be found desirablefor special uses.

An examination of the curve A of Fig. 2 will show that the gridrectification of tube 1 gives a substantially linear response for ashort range of small signal voltages, but that beyond a certain point,rectification occurs in the plate circuit of tube 1, and theplate-current-grid-voltage characteristic itself departs from linearity(usually both effects occur) and the output voltage no longer increasesas a linear function of the applied voltage. 2 is indicated by curve Bwhich shows a longer range of linear response for plate rectificationbut substantially no rectification or nonlinear rectification iseffected at signal voltages corresponding to the range over which lineargrid circuit rectification is obtainable. The curve C for the outputvoltage E of the complete rectifier stage shows that linearrectification may be efiected at signal voltages from zero up to themaximum value corresponding to linear plate circuit rectification. Byadjusting the incoming carrier voltage to bring the point of operation.to the center of the linear portion of curve C,

any modulation of the carrier up to one huns dred per cent will bereproduced faithfully in the amplitude variation of the stage outputvoltage E. The rectified voltage E which-is developed acrossthe gridcondenser 6 is a linear function of carrier voltages falling outside ofas well as those falling within the range of linear grid circuitrecification. The variation of voltage E with increasing carrier voltageis shown by curve D of Fig. 3, and it will be apparent that thisrectified voltage may be employed, if desired, for the automatic controlof the transmission through a carrier wave amplifier which will usuallybe associated with the detector stage.

The present invention is to be distinguished from the usual gridrectification circuits which, with increasing signalstrcngth,,iproduce.plate rectification in opposition to the gridrectifica tion. In accordance with the present invention, the rectifiedvoltages resulting from plate rectification and from grid rectificationare combined in additive relation, and not in opposition.

I claim:

1. In a rectifier stage, a vacuum tube and associated circuit elementsconstituting a grid circuit-rectifier, a second vacuum tube andassociated circuit elements constituting a plate circuit rectifier, asource ofsignal voltage, means,

including a pair of independent condensers connected to differentpotential points of said source for impressing an alternatingv signalvoltage in parallel upon said rectifiers, and a stage output circuitconnected to said rectifiers to combine in additive relation therectified voltages developed in the respective rectifiers.

2. The invention as set forth in claim 1 in combination with means foradjusting the rela-' tive magnitudes of the rectified voltages deliveredto said stage output circuit.

3. A rectifier stage comprising two vacuum tubes, circuit elementsproviding for said tubes input circuits which are in parallel as regardsincoming signals, an output circuit for each'of said tubes, means in thecircuits of the individual tubes to produce grid circuit rectificationin one tube and plate circuit rectification in the second tube, a stageoutput circuit fed from the output circuits of the individual tubes,andindependently adjustable means in the output circuits of said tubes forregulating the feeding of rectified The operation of the tube signalsfrom each tube to said stage output circuit.

4. A rectifier stage comprising two vacuum tubes having input circuitsin parallel, a pair of independently adjustable audio frequencyimpedances serially connected between the anodes of said tubes, aconnection from the junction of said impedances to the cathodes of saidtubes, means'in one input circuit to cause the tube associated therewithto operate as a grid circuit rectifier, means in the other input circuitto cause the tube associated therewith to operate as a plate circuitrectifier, and a stage output circuit across which is developed at leasta part of the rectified potentials established in the individualimpedances.

5. In a radio receiving circuit, a source of signal modulated carrierfrequency energy, a

signal responsive circuit, a space discharge device in combination withcircuit elements constituting a grid circuitrectifier, a second spacedischarge device in combination with circuit ele.-- ments-constituting aplate. circuit rectifier,

means including a pair .of independent condensers connected to differentpotential points of said source for impressing energy from saidfirst-named source in parallel uponsaid rectifiers for causingrectification thereof, in both said rectifiers, and means for combiningin additive relation the rectified voltages developed in the respectiverectifiers.

6. In a radio receiving circuit, a high frequency circuit, a signalresponsive circuit, a space discharge device .and associated circuitelements constituting a grid circuit rectifier, a second space dischargedevice and associated circuit elements constituting a-plate circuitrectifier, both said space discharge devices and associated'. circuitsbeing connected between said high frequency circuit and said signalresponsive circuit, adjustable means .for capacitatively connecting thegrid circuit of the plate circuit rectifier device to said highfrequency circuit, said, signal responsive circuit being adaptedtoreceive, combined in additive relation, the rectified voltages developedin the respective rectifiers.

7. In combination with a detector. stage including: a pair of tubes,a'signal circuit, a load circuit; an adjustable connection to saidsignal circuitfrom thev grid .of one. of the tubes, said connectionincluding a network renderingsaid one tube a grid circuit rectifier, asecond 'adjustable connection including acondenserbetween saidsignalcircuit and the grid of the' remainingftube, means. associated. with thesaid remaining tube rendering it an anode circuit rectifier, and acom'monoutput circuit coupling the anodes of said tubes to said loadcircuit.-

8. In combination with a detector stage including a pairof tubes,asignal circuit, a load circuit, an adjustable connection'to said signalcircuit from the grid of one of the tubes, said connection including anetwork rendering said one tube a grid circuit rectifier, a secondadjustable connection including a condenser between said signal circuitand the grid of the remaining tube, means associated with the saidremaining' tube rendering it an anode circuit rectifier, a common outputcircuit coupling the i its 9. A detector stage comprising a pair oftubes having a common signal input circuit and a common output circuit,means associated with the tubes to operate one as a grid rectifier andthe other as a plate rectifier, means for independently adjusting theconnection between the grid of each tube and points of high alternatingcurrent potential of substantially like phase on said input circuit, andmeans for independently adjusting the detected outputs of said tubes.

10. A detector stage comprising a pair of tubes having a common signalinput circuit and a common output circuit, means for independentlyadjusting the connection between the grid of each tube and points ofhigh alternating current potential on said input circuit, and means forindependently adjusting the detected outputs of said tubes, means foroperating one of the tubes as a grid circuit rectifier, means foroperating the other tube as an anode circuit rectifier, the detectedoutputs of said tubes being combined in additive relation in said outputcircuit.

11. In combination in a radio receiver, a detector stage comprising apair of tubes having common signal input circuit and a common outputcircuit, means for connecting the grid of each tube to points of highalternating current potential on said input circuit, means for operatingone of the tubes as a grid circuit rectifier, means for operating theother tube as an anode circuit rectifier, the detected outputs of saidtubes being combined in additive relation in said output circuit, acarrier wave amplifier having its output coupled to the said commoninput circuit, and means for impressing upon the said carrier waveamplifier a rectified voltage developed in the grid circuit of said gridrectifier, said rectified voltage varying linearly with applied signalvoltage.

KNOX CHARLTON BLACK.

